Packet switched networks transport streaming media, such as video and audio, from a media source to multiple receivers. The packet switched networks, however, may use a quality-of-service scheme that may significantly delay or drop some packets. Retransmission may be used to retransmit the dropped or delayed packets to receivers. Receivers may send negative acknowledgement (NACK) messages to report that packets have not been received. After receiving the NACKs from the receivers, a retransmission server attempts to repair as many packets as possible using unicast and/or multicast retransmissions. Considering the high bandwidth nature of video streams, there is a high risk of NACK implosion on the server if every receiver asks for retransmissions during a short time period. Sending unicast retransmissions to all requesting receivers may not be feasible. Also, sending a large number of unicast retransmissions may use significantly more bandwidth than multicast retransmission.